The present invention is directed to fluid movers and, more specifically, to a shrouded axial flow fan for moving fluids, such as air, from a first location to a second location.
Ventilation systems used in many commercial settings are required, either by code or by functional specifications, to have certain minimum airflow rates. For example, in commercial buildings, a minimum level of airflow is required to maintain a healthy air quality within the building. Similarly, in other applications, such as clean rooms, a certain level of airflow must be maintained to allow adequate filtration and removal of airborne particulate.
In addition to the air flow rate provided by various fans, other factors can affect the selection of a particular fan shroud and fan for a specific location. A few additional factors commonly used to select an appropriate fan are the efficiency of the fan, the size of the motor required by the fan and the noise generated by the fan shroud and fan combination.
Airflow in conventional axial fans is generated along the outer radial edge of the fan blades, resulting in reduced airflow through the center region of the fan and increased air turbulence. The increased air turbulence reduces fan efficiency and increases the noise generated by the fan.
A fan shroud that surrounds the blades of a fan will generally improve the flow of air through the fan. However, the motor size, air flow efficiency, noise generated by the fan, and related factors continue to be problematic in the industry.
According to the invention, a fan shroud for an axial flow fan comprises a generally annular main body having an inlet end, an outlet end, and an inner surface defining a fluid flow path between the inlet and outlet ends. The inner surface includes first and second conical sections that converge toward the outlet end, and a diverging section that diverges toward the outlet end. The second conical section is located between the first conical section and the diverging section. With this arrangement, turbulent fluid flow through the fan shroud between the inlet end and outlet end is minimized. Preferably, a first converging angle of the first conical section with respect to a plane transverse to the direction of fluid flow at the inlet end is less than a second converging angle of the second conical section with respect to the plane.
Further according to the invention, an axial flow fan is positioned in the fan shroud. The axial flow fan includes a central hub and a plurality of fan blades extending radially from the hub. Preferably, the central hub is generally aligned with the second conical section.
Each fan blade has a first side that generally faces the inlet end and a second opposing side that generally faces the outlet end. The first side of each fan blade extends into the first conical section and the second side of each fan blade extends into the diverging section.